detecting a unit is picked

For my map i have 4 custom races and I need a way for them to pick their race; I chose having them select the unit. How would I do this?

You could either make a dialog so they can select there race by clicking a button.

Or you could take a part of your map, create some Circle of Powers or whatever, and put the builder of the race behind the circle of power, when the unit enters the circle they get that race

o yea... I thought of that too, but I could've sworn there was a "A unit is picked" event. Never could Find it though, and it's way too complicated right now. I'm just gonna go with the circle of power thing.

Do you mean by "picked" as in Click on?

A unit is selected event?